Referring to a recent trend for a down-sized or multifunctional electronic equipment, high-density or fine technology of the wiring pattern have been pursued for a circuit board. One of known means for achieving such condition is to form a circuit board in a multilayer. As shown in FIGS. 98(a) and 98(b), in the circuit board formed by stacking a plurality of wiring layers, generally, the conduction is made between the respective layers through a small hole such as a through hole or a non-through hole (below, a hole) of which inner wall is covered or filled with a conductive layer, and which is referred to as a through hole 31, a via hole 32, or an interstitial via hole 33.
FIG. 99 is a schematic view of the hole as seen from the top. In the periphery of the hole 17, a conductive layer referred to as a land 18 is formed. There are various kinds of the land shape such as angular, circular, elliptical, and deformed shape. However, the circular land is frequently used because of the occupied area thereof or the simple use of a circuit design. In order to cope with the trend for the high density, a landless, or narrow land width hole are required.
A method of manufacturing a circuit board includes a subtractive method, an additive method and a semiadditive method. In the subtractive method, an etching resist layer is provided over a circuit portion of an insulating substrate having a conductive layer formed on its surface, and a conductive layer over a non-circuit portion which is exposed is removed by etching so as to form a circuit. In the additive method, a plated resist layer is formed on a non-circuit portion of a surface of an insulting substrate and a conductive layer is formed in a portion corresponding to a circuit portion by a nonelectrolytic plating processing. In the semiadditive method, a plated resist layer is formed on a non-circuit portion of an insulating substrate having a thin conductive layer on its surface, while a conductive layer is formed on a portion corresponding to a circuit portion by an electrolytic plating processing. Thereafter, the plated resist layer on the non-circuit portion is removed and the thin conductive layer on the non-circuit portion is then removed so as to form a circuit by a flash etching processing.
The etching resist layer and the plated resist layer are formed by the methods such as a screen printing method, a photofabrication method, having an exposing and developing step using a photosensitive material, or an ink jet method. In the case in which a landless hole or a hole having a small land width is to be formed, it is important to carry out an alignment in a process of a perforation processing, the screen printing method, the exposing step or the ink jet method. Especially, in the case of forming the landless hole or the hole having a small land width, which are required for a high density circuit board, it is necessary to realize very high precision in an alignment. As shown in FIG. 99, the most desirable alignment for a land should have such a shape as to have a uniform width in all directions of the hole. In other words, the desirable manner is such that the hole and the land make the concentric circles. However, there is a problem in that the hole and the land are not the concentric circles as shown in FIG. 100 when the alignment is not accurate.
FIGS. 100(a) and 100(b) show the schematic plan views, each illustrating a positional shift between the hole and the land in the case. The positional shift at a distance X is generated each in the hole having a small land width in FIG. 100(a), and in the hole having a large land width in FIG. 100(b). Although the land is formed around the hole in the hole having the large land width in FIG. 100(b), the land is cut away by the hole portion in the hole having the small land width in FIG. 100(a), resulting in a problem of impossibility to form a hole having a small land around a whole outer periphery of the hole. Under the conventional circumstance, the precision in the alignment has a limit due to precision in the perforation processing, the expansion of a substrate or a change in a dimension of a photomask for an exposure. Moreover, the hole to be formed on the high density circuit board has a large number of diameters and the number of the holes is very large. For these reasons, it has been very difficult to accurately carry out the alignment with respect to all the holes. As described in JP-A-3-236956 and JP-A-7-7265, accordingly, the circuit design has a problem for employing a large land width regardless of the requirement of a landless hole or a hole having a small land width for the high density circuit board.
It is an object of the invention to provide a method of manufacturing a circuit board such as in a subtractive method, an additive method or a semiadditive method, which solves the problem of the positional shift between a land and a hole, being caused by an alignment in the formation of an etching resist layer and a plated resist layer. Such a method can be employed for a landless hole or a hole having a small land width, which is required for a high-density circuit board.